Fluorocarbon-containing copolymers have been used as binding agents, wetting agents, surfactants and coating additives in a variety of applications. Fluorocarbon-containing copolymers made by conventional free radical polymerization methods have inevitable shortcomings as it is difficult to control their molecular weight distribution and composition in order to optimize their desired physical properties. For example, the common problem of poor control of molecular weight distribution can result in a high molecular weight “tail”, which can give poor flow properties due to the high viscosity that results. Conversely, poor binding properties can result when too much of a low molecular weight “tail” is present.
U.S. Pat. Nos. 5,397,669 and 5,283,148 disclose an electrostatic liquid toner imaging process that uses a liquid toner comprised of a perfluorinated solvent and a polymer containing highly fluorinated units. The polymer was prepared using traditional free radical polymerization techniques and was characterized as having a polydispersity of 4.
U.S. Pat. No. 3,407,247 discloses fluoro olefin block copolymers prepared by traditional free radical polymerization of a (meth)acrylic monomer to form a prepolymer which is subsequently reacted with a fluoro olefin. While block copolymers were formed to some extent, the resulting block copolymers inherently vary widely in block length and molecular weight leading to a wide compositional variation and distribution as well as a large polydispersity.
U.S. Pat. No. 5,026,621 discloses a toner for electrophotography which includes a block copolymer binder resin comprised of a fluoroalkyl acryl ester block and a fluorine-free vinyl or olefin monomer block. The block copolymers were made using a unique peroxypolyether initiator, which is then used to initiate a first free radical polymerization, forming a peroxypolymer, which initiates a second free radical polymerization. While block copolymers are formed, the resulting block copolymers inherently vary widely in block length and molecular weight, as well as having a wide compositional variation, wide polymer composition distribution and a large polydispersity.
U.S. Pat. No. 5,478,886 discloses alkyl α-fluoroacrylate ester block copolymers prepared by group transfer polymerization techniques. The block copolymers have a polydispersity of less than 2 and do not contain any initiator residue. The disclosure is limited to fluoroacrylate monomers as the fluorocarbon monomer. These types of block copolymers are used primarily in the electronics industry as photoresists. The block copolymers are particularly subject to photodegradation.
U.S. Pat. Nos. 5,629,372; 5,705,276; and 5,914,384 disclose coating compositions comprising an alkyl (meth)acrylate/fluoroalkyl methacrylate random copolymer and a crosslinking agent. The materials disclosed were suggested for use as clear coating compositions for application over a pigmented base coat.
The use of conventional, i.e., non-living or free-radical (co)polymerization methods to synthesize (co)polymers provides little control over molecular weight, molecular weight distribution and, in particular, (co)polymer chain structure. In the example of fluoroalkyl methacrylate random copolymer described above, the potential surface tension effect of the fluoroalkyl methacrylate is muted as it is randomly dispersed along the polymer backbone.
U.S. Pat. Nos. 5,807,937, 5,789,487 and 5,763,548, and International Patent Publication Nos. WO 98/40415, WO 98/01480, WO 97/18247 and WO 96/30421 describe a radical polymerization process referred to as atom transfer radical polymerization (ATRP). The ATRP process is described as being a living radical polymerization that results in the formation of polymers having predictable molecular weight and molecular weight distribution. The ATRP process also is described as providing highly uniform products having controlled structure (i.e., controllable topology, composition, etc.). The '937 and '548 patents also describe (co)polymers prepared by ATRP, which are useful in a wide variety of applications including, for example, dispersants and surfactants.
A number of initiators and macroinitiator systems are known to support ATRP polymerization. These initiators are described, for example, in U.S. Pat. Nos. 5,807,937 and 5,986,015. U.S. Pat. No. 5,807,937 discloses a number of initiators, including halide groups attached to a primary carbon. Halides attached to primary carbons are known as efficient initiators in ATRP processes. U.S. Pat. No. 5,986,015 discloses polymer macroinitiators prepared from vinyl chloride and another monomer, and their use in preparing graft (co)polymers with low polydispersity.
It also is desirable to have multiple initiation sites on an initiator in order to create unique branched (co)polymer structures, such as star (co)polymers. Such (co)polymers have a variety of practical applications, including as a resin component of a film-forming coating composition. These unique (co)polymers also will find use in the health care or cosmetics industries, for instance, as materials for bioengineering. (Co)polymers of low polydispersity (Mn/Mw) are also desirable not only for their structural regularity and related usefulness in producing defined block and gradient (co)polymer structures, but also for their unique physical characteristics. For instance, a star (co)polymer having low polydispersity is a high molecular weight material having low viscosity in solution.
There remains a need for copolymers that have reliable compositions and predictable molecular weight, polydispersity and surface tension lowering effect. Such copolymers can overcome the deficiencies of the copolymers of the prior art.